This invention relates to sustained-release pharmaceutical formulations, and more particularly to oral acetaminophen sustained-release formulations for providing extended therapeutic relief.
Many medical conditions are best treated by administration of a pharmaceutical in such a way as to sustain its action over an extended period of time. For example, this kind of pharmaceutical administration can be useful for treating chronic pain, such as that associated with rheumatic or arthritic conditions. Sustained-release dosage forms can also be used beneficially in the administration of antiarrythmics, antihypertensives and other drugs whose sustained action is important to their efficacy.
Many physiological factors influence both the gastrointestinal transit time and the release of a drug from a controlled release dosage form, and thus influence the uptake of the drug into the systemic circulation. Dosage forms should therefore be designed so that such variable factors do not compromise the efficacy and safety of the product. Ideally, such sustained-release dosage forms should release the active pharmaceutical ingredient at a controlled rate such that the amount of active pharmaceutical ingredient which is available in the body to treat the condition is maintained at a relatively constant level over an extended period of time. That is, it is desirable that active pharmaceutical ingredient be released at a reproducible, predictable rate which is substantially independent of physiological factors which can vary considerably among different individuals and even over time for a particular individual.
The release of active pharmaceutical ingredient from a controlled release dosage form is generally controlled either by diffusion through a coating, by diffusion of the agent from a monolithic device, or by erosion of a coating by a process which is dependent upon enzymes or pH. Because such factors can vary from time to time for a particular individual, and can also vary from one individual to another, enzymes or pH dependent sustained-release pharmaceutical formulations do not provide a reproducible rate of release of the active pharmaceutical ingredient, and thus do not minimize intra-subject and inter-subject variation in bio-availability of the active ingredient.
Certain medical conditions are most desirably treated with a dosage form which provides both immediate and extended therapeutic effect while reducing the number of doses necessary, thereby making therapy more convenient. Known examples of pharmaceutical formulations which provide both immediate and sustained-release of an active pharmaceutical ingredient are disclosed in U.S. Pat. No. 4,574,080 to Roswall et al. and U.S. Pat. No. 4,971,805 to Kitanishi et al. Each of these patents disclose a pharmaceutical formulation comprised of a quick releasing component and a slow releasing component, wherein release of the active pharmaceutical ingredient from the slow releasing component relies on a pH dependent diffusion control mechanism such as an enteric coating. Such formulations have the disadvantage of releasing the active pharmaceutical ingredient at a variable rate dependent upon the pH of the gastrointestinal fluids in which it is contacted, which can vary from subject to subject and can vary for a particular subject.
U.S. Pat. No. 4,666,703 to Kopf discloses a quick-disintegrating pharmaceutical tablet containing an active substance in a granular delayed release form comprising a pharmaceutically active substance in granular form which is coated with a mixture of a polyacrylate, such as an aqueous dispersion of an ethyl acrylate-methyl methacrylate copolymer, and ethyl cellulose, which are subsequently compressed into tablets. Kopf, however, does not provide both immediate and sustained-release of the active pharmaceutical ingredient.
Roswall et al. (U.S. Pat. No. 4,574,080) discloses a pharmaceutical orally administrable controlled release multiple-units formulation form in which individual units comprise coated cores containing an active substance which is subjected to controlled release as a result of coating the cores with a water-insoluble, but water-diffusible controlled release coating. The units include instant release particles of an active substance adhered to the surface of a controlled release coating, the particles being at least one power of 10 smaller than the coated core.
U.S. Pat. No. 5,055,306 to Barry et al. discloses a pharmaceutical tablet comprised of granules having a core including an active substance and an encapsulating coating comprising 100 parts by weight of water-swellable acrylic polymer and 20 to 70 parts of water-soluble hydroxylated cellulose derivative. The combination of water-swellable acrylic polymer and water-soluble hydroxylated cellulose derivative provides a coating having release characteristics which are pH dependent, i.e. an enteric coating.
A two layer acetaminophen tablet is available in which one layer is comprised of uncoated, quick release acetaminophen particles, and the other layer is comprised of sustained release acetaminophen. Two compression steps are required to make the tablet, and the sustained release coating is pH dependent.